Oven construction for molten salt shower heating



Nov. 22, 1966 H. J. SNELSON OVEN CONSTRUCTION FOR MOLTEN SALT SHOWER HEATING Filed July 3. 1964 HOWARD J. SNELsoN ,sMwM' AHornf S United States Patent "ice 3,287,005 OVEN CONSTRUCTION FOR MOLTEN SALT SHOWER HEATING Howard J. Snelson, Columbus, Ohio, assignor of one-half to Amos-Thompson Corporation, Edinburg, Iud., a

corporation of Indiana Filed July 3, 1964, Ser. No. 380,160

3 Claims. (Cl. 263-40) This invention relates generally to heating ovens or enclosures where liquid such as a molten salt is used as the heat transfer medium, and in particular to construction of an oven adjacent its door which prevents the build-up of solidified salts on the door'or adjacent oven inner surfaces which would otherwise interfere with door opening and closing.

In the rotational casting of synthetic resins it is well known in the art to move, usually in a circular path, closed, charged molds into'and out of a series of processing stations. At least one of these stations is, conventionally, an oven for heating the mold and within which the mold is rotated on two perpendicular axes. Examples of the type of installation referred to are disclosed in US. Patents 3,044,124 and 3,115,680.

In such installations various heating means may be utilized in conjunction with the oven enclosure. One method for heating the molds while in the oven enclosure utilizes a shower of molten salt directed at the mold or molds within the oven. The salt, a commercially available mixture of metallic salts, and liquid at temperatures of the order of 500 F., has a high thermal efficiency (about three'times that of hot air) and when showered on the mold, stays in contact with the mold instead of rebounding off as is the case of a hot air stream. The liquid salt also flows around or conforms to irregularly shaped molds to a degree impossible to achieve with a hot air stream. The use of molten salt as a heat transfer medium thus has definite advantages for use in rotational casting ovens.

In the past the use of molten salt has, however, encountered one serious difliculty. In the mold showering process molten salt splashes onto the inner surfaces of the oven enclosure and on the inner surface of the movable door for the oven enclosure. The salt solidifies on these surfaces and in a relatively short time, solidified salt builds up, particularly on the door and to some extent on adjacent surfaces, sufiiciently to interfere with movement of the door between open and closed positions. For ovens utilized in actual production processes, the process delay caused by such solidified salt buildup and its necessary removal is highly disadvantageous.

The concept of the present invention provides a steel plate or shield on the inner surface of the movable oven door which is spaced somewhat from the door panel proper. The shield is fastened to the door along one margin, the upper margin of the door as herein disclosed, and hangs from this support in spaced relation to the inner surface of the door panel. Since the shield is spaced slightly from the door surface, direct heat transfer to the door by conduction is somewhat impeded. The shield thus has reduced thermal inertia and heats and cools relatively rapidly and therefore expands and contracts in response to temperature change relatively rapidly. The rate of thermal expansion and contraction differs substantially from the thermal expansion rate of the solidified salt deposited on the inner surfaces of the door and, as a result salt, deposited on the inner face of the door protected by the shield, is shucked off the shield and drops to the oven floor. No build-up of salt on the shicded surfaces occurs even after prolonged use of the oven.

It is the primary object of the present invention to pro- 3,287,005 Patented Nov. 22, 1960 vide a construction for'the door and adjacent surfaces of a salt shower enclosing oven which eliminates accumulating deposit or build-up of solidified salt on the door and oven surfaces.

This and other objects will become apparent as the description proceeds with reference to the accompanying drawings in which:

FIG. 1 is a schematic, top plan view, greatly reduced, of 'a rotational molding apparatus installation with an oven embodying the construction of the present invention.

FIG. 2 is a perspective view of the oven shown in FIG- URE 1.

FIG. 3 is a sectional view taken generally along the line 33 of FIGURE 2.' 7

FIG. 4 is an enlarged fragmentary view showing the shield member utilized in the oven construction.

Referring initially to FIGURES 1, 2 and 3, the oven whose construction incorporates the shielding arrangement'of the present invention is indicated generally at 10. The oven is of generally rectangular configuration having side walls 11, a rear wall 12 and a curved front wall 13. As indicated in FIGURES 2 and 3 the lower portion of the front wall and of each of the side walls 11 are cut away to provide an opening which is closed by the vertically movable oven door 14. The oven door 14 is generally U-shaped, having an inwardly concave front face 14a and side faces which extend parallel to and spaced somewhat from the side faces 11 of the oven. A suitably powered hoist arrangement, fastened to the door by means of cables 16 provide for the vertical raising of the door so in FIGURE 2 is located at the rear of the oven and serves v to recirculate molten salt from the sump to the shower heads 21'. Suitable means are also provided for maintaining the molten salt at the proper temperature. The salt used may be a mixture of commercially available metallic salts requiring a temperature of approximately 500 to maintain them in low viscosity liquid form, the salt solidifying at about 310 F.

Referring now particularly to FIGURE 1, there is shown indicated generally at 24 a rotational molding apparatus consisting of a rotating frame 26 having extending radially therefrom mold carrying arms 27. Each of the arms 27 (although only one is shown in completed form in FIGURE 1) carries at its outer end a closed and charged mold indicated generally at 28. A drive means, schematically indicated at 29 in FIGURE 1, may be provided for rotating the mold 28 about its own axis and also about the axis of the arm 27 while the mold is in the oven. During this compound rotation of the charged mold within the oven, the necessary heating of the mold is provided by the shower of molten salt which drenches the outer surfaces of the mold during its rotation. The rotating frame, the arms 27 and the molds carried thereby are disposed within a circular pit at the front of the oven so that with the oven door 14 in its lowermost or closed position the arm '27 may extend within the oven. The indexing of the arms 27 so as to move the molds carried thereby into and out of the oven may be automatically controlled so that when the desired rotation period within the oven is completed, the oven door is raised to open position, rotation of the molds is stopped and the arms are indexed so as to bring a new unheated mold into the oven while moving the heated mold into a cooling station (not shown) and subsequently to an unloading station. When an unheated mold is in place in the oven, the doors are automatically lower to closed position, rotation of the mold on two axes begins and the molten salt spray within the oven directed at the mold is commenced. Automatic sequencing of the operations requires that the individual component steps be systematically completed. Any build-up of solidified salt at the door of the oven, so as to interfere with its operation, thus becomes highly detrimental to automatic sequencing of the apparatus.

Referring now particularly to FIGURE 4, which is an enlargement of the side wall-door junction shown in FIG- URE 3, the panel of the door 14 is formed of an outer steel shell enclosing suitable thermal insulation 31. The inner face 14b of the door 14 is shielded or covered by a steel shield 32. The steel plate or shield 32 is rigidly secured to the upper margin of the door 14 at 33 and extends in parallel spaced relation to the inner surface 14b of the door. If necessary, brackets or spacers 34 may be provided at intervals between the inner surface vof the shield 32 and the surface 14b of the door. The plate 32 forming the shield extends the length of the door and is preferably formed of twenty gauge body steel with the spacing between the plate 32 and the surface 14b of the door being approximately one-half inch. Since the plate 32, isolated somewhat from the door panel 14, has relatively small thermal inertia, it is heated and cooled relatively rapidly with the cycling of the oven and the consequent relatively rapid rate of thermal expansion and contraction causes solidified salt accumulating on the outer face of the shield plate 32 to be shucked off the plate, the loose accumulations of salt falling into the sump 19 atthe base of the oven. The presence of the shield plate 32 prevents an accumulation of solidified salt on the door which might interfere with raising and lowering the door by bridging the clearance, indicated at 36 in FIGURE .4, between the door 14 and the oven side walls 11. The dif-- ference in appearance between the surface of the shield and the adjoining unshielded inner surfaces of the oven (where deposits of accumulated salt can be tolerated since movement of the oven door is not involved on these surfaces) is quite dramatic after prolonged use of the oven. The reason for such difference in accumulation of salt on the shielded and unshielded surfaces is believed to be caused by the difference in thermal expansion between the shield and the salt accumulations referred to previously. It will be understood that, while the shield 32 is shown mounted only on the door surface, such a shield,

hung from the upper margin of the oven walls might also be used on the Wall surfaces of the oven itself should that be desirable and the scope of the invention is intended to include such analogous uses of the shield.

v 1. In an oven having an access opening and adapted to enclose an article to be subjected to a molten salt shower.

Within the oven for heating the article, a door movable for opening and closing the oven access opening, a plate secured to one margin of said door and extending in parallel spaced relation to the inner surface of the door, said plate shielding said inner surface of the door from deposits of solidified salt and shucking off such deposits to prevent their interference with opening or closing movement of said door.

2. In an ovenhaving an access opening and adapted to enclose an article to be subjected to a molten salt shower within the oven for-heating the article, a door movable for opening and closing the oven access opening, a plate secured to one margin of said door and extending in parallel spaced relation to the inner surface of the door,

said plate having a coefiicient of thermal expansion sub-. stantially differing from that of salt of said shower when 1 solidified, said plate therebyshielding said inner surface. ofthe door from deposits of solidified salt and shucking,

ofl? such deposits to prevent their interference. with openmg or closing movement of said door.

3. In an oven having side walls with an accessopening therein and adapted to enclose an article to be sub-;

jected to a molten salt shower within the oven for heatopening, a steel plate secured to one margin of said door and extending in parallel spaced relation to the inner surface of the door, said plate shielding said inner surface. of the door from deposits of solidified salt and shucking ofif such deposits to prevent their interference with opening or closing movement of said door.

References Cited by the Examiner.

UNITED STATES PATENTS 1,951,420 3/1934 Jones 165- 84 2,464,508 3/1949 Holden 263 11 2,531,344 11/1950 Polad -180 2,559,763 7/1951 Ginder et al. 2635O FREDERICK L. MATTESON, 111., Primary Examiner. JOHN CAMBY, Exar niner. A. D. HERRMANN, AssistantExaminer. 

1. IN AN OVEN HAVING AN ACCESS OPENING AND ADAPTED TO ENCLOSE AN ARTICLE TO BE SUBJECTED TO A MOLTEN SALT SHOWER WITHIN THE OVER FOR HEATING THE ARTICLE, A DOOR MOVABLE FOR OPENING AND CLOSING THE OVEN ACCESS OPENING, A PLATE SECURED TO ONE MARGIN OF SAID DOOR AND EXTENDING IN PARALLEL SPACED RELATION TO THE INNER SURFACE OF THE DOOR, SAID PLATE SHIELDING SAID INNER SURFACE OF THE DOOR FROM DEPOSITS OF SOLIDIFIED SALT AND SHUCKING OFF SUCH DEPOSITS TO PREVENT THEIR INTERFERENCE WITH OPENING OR CLOSING MOVEMENT OF SAID DOOR. 